Magnetic fields

A magnet creates a magnetic field around it. You cannot see a magnetic field, but you can observe its effects. A force is exerted on a magnetic material brought into a magnetic field. The force is a non-contact force because the magnet and the material do not have to touch each other.

Finding magnetic fields

You can use a plotting compass or iron filings to detect a magnetic field:

  1. put a piece of paper over a magnet (this stops the iron filings sticking to the magnet)
  2. sprinkle iron filings onto the paper
  3. gently tap the paper to spread the filings out
  4. observe and record the results
Iron filings showing the magnetic field of a bar magnet
Iron filings show the magnetic field around this bar magnet

Drawing magnetic field diagrams

It would be difficult to draw the results from the sort of experiment seen in the photograph, so we draw simple magnetic field lines instead.

Magnetic fields go from the north to the south pole of a magnet

In the diagram, note that:

  • each field line has an arrowhead on it
  • the field lines come out of the north pole and go into the south pole
  • the field lines are more concentrated at the poles

The magnetic field is strongest at the poles, where the field lines are most concentrated.

Field lines also show what happens to the magnetic fields of two magnets during attraction or repulsion.

Field lines lead from one magnet to the other when the magnets attract each other.Field lines lead from one magnet to the other when the magnets attract each otherField lines do not lead from one magnet to the other when the magnets repel each other.Field lines do not lead from one magnet to the other when the magnets repel each other